Cell measurements in unlicensed frequency bands

Abstract

This disclosure relates to performing cell measurements in unlicensed frequency bands and/or in channels with interference. According to some embodiments, a wireless user equipment (UE) device may define a reference symbol vector for a cell. Each respective element of the reference symbol vector may correspond to a respective subcarrier of the cell that carries a respective reference symbol. The UE may perform channel estimation at each respective element of the reference symbol vector. The UE may estimate the cell strength of the cell by cross-correlating channel estimates of different elements of the reference symbol vector.

What is claimed is: 
     
       1. A method for a wireless user equipment (UE) device to perform cell measurements, comprising:
 by the UE device:
 defining a reference symbol vector for a cell, wherein each respective element of the reference symbol vector comprises a respective subcarrier of the cell that carries a respective reference symbol; 
 performing channel estimation at each respective element of the reference symbol vector; 
 estimating a cell strength of the cell in a first manner by cross-correlating channel estimates of different elements of the reference symbol vector. 
 
 
     
     
       2. The method of  claim 1 ,
 wherein performing channel estimation at a respective element of the reference symbol vector comprises multiplying a signal received at the respective subcarrier of the element by a conjugate of the respective reference symbol carried by the respective subcarrier. 
 
     
     
       3. The method of  claim 1 ,
 wherein the reference symbol vector comprises elements corresponding to subcarriers comprised in a plurality of orthorgonal frequency-division multiplexing (OFDM) symbols of a subframe of the cell. 
 
     
     
       4. The method of  claim 1 ,
 wherein the cell is on a channel in an unlicensed frequency band. 
 
     
     
       5. The method of  claim 1 , further comprising:
 estimating cell strength of each of a plurality of cells in the first manner by cross-correlating channel estimates of different elements of respective reference symbol vectors for each of the plurality of cells. 
 
     
     
       6. The method of  claim 1 , further comprising:
 estimating the cell strength of the cell in a second manner by autocorrelating channel estimates of subcarriers of the cell which carry reference symbols. 
 
     
     
       7. The method of  claim 6 , further comprising:
 reporting a difference between the cell strength of the cell estimated in the first manner and the cell strength of the cell estimated in the second manner to a serving cell of the UE device. 
 
     
     
       8. The method of  claim 1 ,
 wherein the cell operates according to Long-Term Evolution (LTE), wherein the cell strength estimation is an estimation of reference signal received power (RSRP) of the cell. 
 
     
     
       9. The method of  claim 1 ,
 wherein cross-correlating channel estimates of different elements of the reference symbol vector is configured to reduce at least one of interference and noise effects from the cell strength estimated in the first manner. 
 
     
     
       10. A wireless user equipment (UE) device, comprising:
 a radio; and 
 a processing element operably coupled to the radio; 
 wherein the radio and the processing element are configured to:
 calculate cell strength of a first cell, wherein the cell strength of the first cell is calculated at least in part by cross-correlating channel estimates of different reference symbol subcarriers of the first cell; and 
 provide an indication of the calculated cell strength of the first cell to a serving cell of the UE device. 
 
 
     
     
       11. The UE device of  claim 10 , wherein the radio and the processing element are further configured to:
 define a reference symbol vector for the first cell, wherein each respective element of the reference symbol vector comprises a respective subcarrier of the cell that carries a respective reference symbol, 
 wherein cross-correlating channel estimates of different reference symbol subcarriers of the first cell comprises cross-correlating channel estimates of elements of the reference symbol vector with each other. 
 
     
     
       12. The UE device of  claim 10 , wherein to calculate the cell strength of the first cell, the radio and the processing element are further configured to:
 perform cell strength sub-calculations on a per path basis based on a number of transmit and receive antennas of the first cell and the UE; and 
 average the per path cell strength sub-calculations to produce an average cell strength estimate. 
 
     
     
       13. The UE device of  claim 12 ,
 wherein the per path cell strength sub-calculations are averaged in a linear manner. 
 
     
     
       14. The UE device of  claim 12 ,
 wherein the per path cell strength sub-calculations are averaged in a weighted manner. 
 
     
     
       15. The UE device of  claim 10 , wherein the radio and the processing element are further configured to:
 perform time-domain averaging of cell strength sub-calculations performed at different times to calculate the cell strength of the first cell. 
 
     
     
       16. The UE device of  claim 15 ,
 wherein the time-domain averaging is performed using an exponential time window. 
 
     
     
       17. A non-transitory computer accessible memory medium comprising program instructions which, when executed at a device, cause the device to:
 define a reference symbol vector for a cell, wherein each respective element of the reference symbol vector corresponds to a respective subcarrier of the cell that carries a respective reference symbol; 
 perform channel estimation at each respective element of the reference symbol vector; 
 estimate a cell strength of the cell in a first manner by cross-correlating channel estimates of different elements of the reference symbol vector; and 
 provide an indication of the cell strength of the cell as estimated in the first manner to a serving cell of the device. 
 
     
     
       18. The memory medium of  claim 17 ,
 wherein the cell is deployed on a channel in an unlicensed frequency band, 
 wherein cell strength of the cell is estimated in the first manner based at least in part on the cell being deployed on a channel in an unlicensed frequency band. 
 
     
     
       19. The memory medium of  claim 17 , wherein when executed at the device, the program instructions further cause the device to:
 estimate the cell strength of the cell in a second manner by autocorrelating channel estimates of different elements of the reference symbol vector; and 
 transmit an indication of the cell strength of the cell as estimated in the second manner to the serving cell of the device. 
 
     
     
       20. The memory medium of  claim 17 ,
 wherein the cell operates according to Long-Term Evolution (LTE), 
 wherein the reference symbol vector comprises elements corresponding to reference symbol subcarriers comprised at least in orthogonal frequency-division multiplexing (OFDM) symbols 0 and 4 of the cell.